This invention relates to reinforced metal-matrix composites and apparatus for their manufacture, and more particularly, to composites comprised of strain-hardenable metal-matrix with elongated reinforcing members dispersed therein and held in position thereby, but selectively and differentially bonded thereto.
Laboratory tests have shown that metal-matrix composites, compared with metals, glasses, ceramics, plastics, etc., offer weight saving in aerospace or other structures of up to 45 percent or more. Composites with reinforcing members made of graphite, ceramics, or other refractory compounds promise to have high strengths, high modulii, and long-life, high-temperature capabilities. A list of matrix metals already employed includes aluminum, magnesium, titanium, beryllium, iron, copper, silver, molybdenum, and nickel. The materials of the reinforcing members also have varied from boron, beryllium, graphite, sapphire, silicon carbide, boron carbide, to stainless steel.
Composite samples have been made which possess ultimate tensile strengths of over 147 ksi and compressive strengths of 300 ksi, but not much ductility. Unfortunately, the field of metal-matrix composites is still backward. The advaces made so far have largely been empirically based. Different production methods have been used. Such methods include vapor deposition, diffusion or roll bonding, liquid metal infiltration, unidirectional melt growth, powder metallury, electroforming, draw cladding, and plasma spraying. However, all are beset by major manufacturing problems. The magnitude of these problems has been almost universally considered to be insurmountable for the next few years.
Foremost among these problems is the difficulty of developing optimum bonding between the matrix and fibers or reinforcing members. The bonding interfaces apparently play a very significant part, if not the key role, in the determination of the resultant composite properties. Thus, observed composite failures mostly occur at or near the matrix-fiber interfaces. It is generally considered that a uniformly strong bonding is essential to the reinforcing mechanism. Too strong bonding, however, appears to cause the composite to be severely limited by the matrix. It is also thought that the fibers must completely wet the matrix (see, e.g., Wainer in U.S. Pat. No. 3,282,658); yet, when this occurs, chemical reactions, interdiffusions, or intermetallic compound formations often result, which cause severe chemical degradations or even destructions of the reinforcing fibers. Other problems with most present composite manufacturing include:
1. fiber nonalignment exceeding 3.degree.; PA1 2. physical or chemical degradation of the fibers, due to processing or reaction with the matrix; and PA1 3. improper control of fiber distribution in the composites.